In many industrial applications it is common to store solid particles in bulk form within a container such as a silo or bunker which has a bin portion (the top part of the container) and hopper (the bottom part of the container). The hopper normally has converging surfaces which terminate in an opening through which the solid particles are to be discharged on an intermittent or continuous basis. In the storing of solid particles in bulk form within containers for subsequent discharge through an opening in the container, various flow problems are often encountered if the physical dimensions of the container have not been correctly designed or are inachievable under present technology for the particular material being handled. In some instances the material will form a bridge, arch, or pipe which obstructs the flow of material from the container. The stability of this obstruction depends upon properties which are controlling the formation of such an obstruction. These properties are normally (but not restricted to) the adhesion between the material and the wall of the container and the internal friction of the particles (a function of size, shape and moisture content of the material). The form of the container is also a material factor. Containers of optimum design can be fabricated for some, but not all, bulk solids if the appropriate physical properties of the solid particles are identified and properly considered during the initial design of the container. An example of one method for determining optimum dimensions for a container for a given material is described in A. W. Jenike, Storage and Flow of Solids, Bulletin 123, Utah Engineering and Experiment Station, University of Utah, 1964.
However, it is not uncommon to find containers which have been incorrectly designed or containers which were designed for one material and are being used for another material having different physical properties. It is also possible to encounter materials for which a suitable container design cannot (with state-of-the-art knowledge) be reached. It is possible in some instances to determine which conditions promote the bridging, arching or piping of the material. A full discussion of the techniques for identifying these conditions and locating them within a given bin or hopper can be found in the Jenike bulletin identified above.
When flow problems are encountered it is often necessary to improve the flowability of the bulk solid in the existing container. Various methods have been proposed for this purpose. One such method involves placement of a flow-corrective insert in the container. These inserts may take the form of a guideplate, tube, spiral chute or cascade conveyers. Use of conical inserts has been suggested and the design and dimensioning of such inserts is described in J. R. Johanson, The Use of Flow-Corrective Inserts in Bins, J. Eng. Ind. (May, 1966).
Other approaches have been proposed and used. These include mechanical devices which are fixed to the wall of the container such as vibrators, inflatable pads inside the containers and the placing of pipes within the containers through which air or other gas may be directed to fluidize the particles and improve their flowability. However, the auxiliary devices mentioned above are not in all instances satisfactory. Many of the flow problems mentioned above can be solved with the present invention which may be inserted into existing containers, without altering the exterior shape of the container, to promote the flow of bulk solid particles by interrupting, in a novel manner, consolidating forces which, absent the apparatus, could cause bridging, arching or piping of the material or in some manner limit or stop flow of the bulk solid particles.